The present invention relates to a breakdowns evaluating test element for evaluating breakdown of semiconductor elements formed on a wafer. Such breakdowns are caused by a wafer's electrification (charge) phenomenon produced during the semiconductor manufacturing process and resulting from charged particles or plasma generated by the semiconductor manufacturing appliance.
There are two types of semiconductor manufacturing appliances. One utilizes thermochemical reaction and the other uses charged particles or plasma. In the case of the later appliance, since the energy of charged particles or the quantity of plasma can be controlled physically, it is possible to process the semiconductor devices more precisely than with the former appliance. In addition, since the semiconductor wafer is maintained at a relatively lower temperature in the charged particles or plasma process, photoresist masks are usable and therefore restrictions in semiconductor circuit design can be reduced. The semiconductor manufacturing appliances utilizing charged particles or plasma include an ion implanting apparatus, a reactive ion etching (RIE) apparatus, an oxygen asher apparatus, etc.
In semiconductor manufacturing appliances utilizing charged particles or plasma, however, there exists a problem. Charged particles are accumulated on oxide films (SiO.sub.2) formed on a semiconductor or electric insulators required for the photoresist forming process, so that precise processing becomes difficult. Further, in cases of excess accumulation, the gate oxide films of semiconductor elements (e.g. transistors) are damaged or brought into breakdown. Since the damage or dielectric breakdown of gate oxide films cannot be repaired, it is indispensable to provide means for preventing semiconductor devices from breakdown resulting from the semiconductor manufacturing appliance which utilizes charged particles or plasma.
As the breakdown prevention appliance, a so-called electron shower (electron flood) system, for instance, is known in the case of the ion implanting appliance. In this system, a wafer to which ions are being implanted is irradiated with an electron beam to neutralize the positive charge accumulated by ions or to reduce the quantity of accumulated electric charge.
In the semiconductor manufacturing appliance which adopts this breakdown prevention countermeasure, it is necessary to periodically test the breakdown prevention effect. An example of the test method is disclosed in Solid State Technology Magazine, pages 151 to 158, Feb. 1985. The charged state of a wafer to which ions are implanted or plasma electric field is applied by the appliance to be tested is measured by a measurement unit including a capacity charge sensor as shown in FIG. 11.
In more detail, with reference to FIGS. 11A to 11C, a sensor electrode 2 is disposed above a tested wafer 1. The output of this sensor electrode 2 is connected to an oscilloscope 3 so that the charged state of the sensor electrode 2 can be monitored as a waveform on the display of the oscilloscope 3.
In measurement, the tested wafer 1 is moved below and in parallel to the sensor electrode 2 in the arrow directions as shown in FIGS. 11A to 11C. In this measurement, since the electric charge opposite in polarity to that charged on the surface of the wafer 1 is induced on the sensor electrode 2, it is possible to monitor the charged state on the wafer 1 as the induced charged state on the display of the oscilloscope 3. For instance, if the wafer 1 is charged positive, since the sensor electrode 2 is induced negative, a positive pulse waveform can be monitored by the oscilloscope 3. By use of this test unit, accordingly, the charged state of the wafer 1 can be known on the basis of the presence or absence or polarity or amplitude of the pulse waveform; that is, it is possible to check whether the electron shower system operates normally or not.
In the above-mentioned test method using the capacity charge sensor, the entire charged state of the wafer 1 is checked macroscopically. Where the wafer 1 is charged negative or positive non-uniformly, as shown in FIG. 12, no pulse is generated as if the wafer 1 is not charged. Further, where the wafer 1 is charged negative as a whole except for a local positive charge, the minor charge is neglected, and the prior-art test unit cannot accurately check the charged state distribution on the wafer 1.
There also exists a method of microscopically checking manufactured wafers. In this method, however, the wafers are tested after all the manufacturing process till ion implantation has been completed. Problems exist in that the tested wafers are wasted and therefore it is uneconomical or it takes much time to test the wafer 1 or the charged state on the wafer cannot be checked accurately according to the wafer's charged state.